Pulse jet fabric filters (PJFFs) are industrial filter buildings located at coal-fired and other types of power plants that produce heave particulate loads in the furnace exhaust gas. The furnace may also be referred to as a boiler (even though the furnace need not generate steam for the present invention to be applicable), and the exhaust gas may be referred to as flue gas for descriptive convenience. The PJFF is used to remove the particulates from the flue gas as part of the “scrubber” exhaust air cleaning system. The PJFF typically contains thousands of long, tubular filter bags in the approximate range of 4 to 10 inches across and 15 to 33 feet (5 to 10 meters) long. The boiler exhaust gas is directed through the filters to remove the particulates from the flue gas, which fall into a hopper under the filter bags for removal and ultimate disposal via rail or truck cars. Each power plant may have multiple furnace units, each having a dedicated PJFF building located adjacent to the furnace for cleaning the flue gas from that particular unit prior to release into the atmosphere. Each PJFF usually includes thousands of individual filter bags and is typically organized into a number of compartments. Each compartment typically contains hundreds of individual filter bags discharging into a common hopper.
For example, an illustrative PJFF for one furnace unit of a commercial coal-fired power plant may include 10 compartments, each terminating in a dedicated hopper. Each compartment may include 816 tubular filter bags, for a total of 8,160 filters in the overall PJFF delivering particulates from the flue gas produced by its associated boiler through 10 hoppers for disposal. The overall PJFF structure typically weighs on the order of a thousand tons. The filter compartments may stand on the order of 40 feet tall, which the overall PJFF building standing on the order of 60 feet to 90 feet.
PJFFs are large industrial structures that are typically custom designed for each furnace unit and assembled on the power plant site. This requires cutting the source materials (such as large casing panels) to the desired sizes and structural welding of the various components in the field. On site construction disturbs the power plant and requires outdoor construction for an extended period of time. The conventional approach to PJFF fabrication includes shipping the large casing panels to the site, temporarily storing them onsite, and extensive cutting, fabrication and structural welding in the field. Field welding generally produces lower overall quality welding (over many welds) and higher costs than shop fabrication, where the environment is controlled and all necessary equipment is available and well-staged (e.g., railroad access, onsite inventory storage, overhead cranes, etc.) Conventional erection is comparatively ad hoc, often requires field modifications from initial plans, and requires many “lifts” by a large crane to position components for welding. This results in a relatively long erection time, particularly to cut the casing panels to size, position and structurally weld all of individual components in place.
Although certain PJFF components have been partially assembled off site in prior designs, the conventional practice is to perform most of the fabrication on site. This is a costly and time consuming process that disturbs the power plant site for an extended period, must typically be completed almost entirely outdoors, and requires locating specialized equipment on site for extended periods. A continuing need therefore exists for more cost effective and efficient approaches to PJFF fabrication.